The present invention relates generally to the field of adjustable rotational position sensors and more particularly to an improved mechanically adjustable sensor assembly which provides spark timing signals for the ignition system of an engine.
Mechanical and electronic ignition systems for internal combustion engines are commonly known to those of average skill in the art. Both of these systems require the sensing of the rotational position of the crankshaft of the engine so that the cylinder spark ignitions will occur when the cylinders are at desired positions during their compression cycles. Prior mechanical ignition systems use a cam which is synchronously rotated by the engine crankshaft and which sequentially delivers a spark signal, through a set of contact points opened and closed by the cam, to contacts which are located at adjustable rotational positions with respect to the axis of rotation of the cam. Commonly, the rotational position of a distributor housing carrying the points and contacts is varied in order to provide for adjusting the occurrence of the spark timing ignition signals with respect to the rotation of the cam. In electronic ignition systems, a rotary body having projections is synchronously rotated by the crankshaft of the engine. The rotational position of this rotary body is then sensed by a variety of sensor devices including photosensitive transistors, magnetic pick-up sensors and Hall sensors. Hall sensors are known to those of average skill in the art and comprise a probe having an active sensor area which develops a signal in response to the presence of a metallic material adjacent to the active sensor area.
In some prior electronic ignition systems, the rotational position of the active sensor area with respect to the axis of rotation of the rotary body is fixed. Adjusting the occurrence of the spark timing signal with respect to the rotational position of the rotary body is then accomplished by either an electronic adjustment in the circuitry processing the Hall sensor signal or a mechanical adjustment which involves rotating the rotational position of the rotary body with respect to the rotational position of the crankshaft of the engine. In the first case, additional electronic circuitry is required to perform the adjustment while in the second case access to the rotary body and additional mechanical structure providing for its rotational adjustment must be provided. In addition, adjustment of the rotary body with respect to the crankshaft would be impractical where the rotary body is located within the block of the internal combustion engine. An alternative solution for providing a rotational position adjustment would be to mount the sensor probe so that its rotational position with respect to the axis of the rotary body would be adjustable. This would be analagous to the mechanical ignition system in which the distributor housing is mechanically rotated to provide an adjustment. Such an alternative solution would also require complex additional mechanical mounting structures for the sensor and would be totally impractical for ignition systems in which the sensor is to be mounted through or within the engine block.